Projection lamp



Dec. 25, 1962 5, PEEK, JR ETAL 3,070,723

' PROJECTION LAMP Filed Jan. 21, 1960 SAA/DFOED c. PEEK JR. 40 WARREN H. HAY

INVENTORS 25 5 VOLTAGE. FOE EATED LIFE BY A'ITORNEY United States Patent 3,070,723 I I, PROJECTION LAMP Sandford C. Peek, Jr.,-South Hamilton, and Warren H. Hay, Beverly, Mass, assignors to Sylvania Electric Products Inc, a corporation of Delaware Filed .ia'n. 21, 1960, Ser. No. 3,758 Claims. (Cl. 313-413) This invention relates to incandescent lamps for projection purposes, that is, for projecting a beam oflight. Such lamps are used, for example, in moving picture and slide projectors. In their most recent forms, such lamps include a metallic reflector in close proximity to an incandescent filament which has the form of a coiled-coil.

We have discovered that the most efiicient form of coil for such lamps is one that operates at between about and 23 volts, and particularly at about 21.5 volts, and that a coil designed for a voltage greateror smaller than that will not be as efficient. Efficiency in such lamps is a factor of great importance because a high elficiency means that a-given amount of light is produced at a lower Watt input to the lamp, thereby causing less heating effect on the film or slide and requiring a smaller blower for cooling the lamp.

The eificiency of the coil can be further increased by 'pulling out one turn on each side of the coil between the main coil and the supporting lead-in wires. This appears to reduce the temperature. gradient along the ends of the coil, thereby reducing preferential etching due to the temperature gradient. 7

In addition, it facilitates control of the total effective filament length by insuring that said length is terminated at a particular turn. The end turns of the filament, beyond thepulled out turn, have a mandrel or so-called spud inside'them, thereby both short-circuiting them and facilitating their attachment to a support wire. The mandrel or spud terminates at about the middle of the axial length of the pulled-out turn, and insures that the termination occurs at that particular turn, and not one on either side of it, as could easily be the-case if the man- 'd-rel were inserted into the closely-wound coilwithout the pulled turn. The importance offixing the exact turn at which 'the effective length of the coil terminates (that is, the turn at which the shorting effect of the spud begins) is indicated by the fact that a variation-of one turn can make a life difference of 7%.

The projection lamp is generally designed for vertical operation with the base down, that is, with the base at the bottom. If the lead-in'wires to the filament extend transversely to the lamp axis in the region in which the filament is attached to them, it is found that having the legs of the filament extend outward from the top of-the coil, that is, from thepa'rt of the coil furthest from the base, rather thanfrom'the' axis of the coil, or the bottom or sid'e,the operation is much better. We findthat under such circumstances, the sag in the turn will bend them outward from ea'ch'e'ther; and not closer together, thereby preventing short-circuiting or overheating. The legs of the coil are preferably attached to the top of the leadin wires.

Other advantages, features and objects of the invention will be apparent from the following specification, taken in connection With the accompanying drawing in which:

FIGURE 1 is a profile view, partly in section, of one embodiment of a lamp according to the invention;

FIGURE 2 is a front view of the same lamp;

FIGURE 3 is an enlarged view, partly in section, of the structure of the filament and its supports; and

FIGURE 4 is a graph showing the variation in light output with filaments of different voltages.

In FIGURE 1, an enclosing tubular glass envelope 1 contains the incandescible coiled filament 2 and the polished metal reflector 3 in position to reflect light from said filament. The reflector can be paraboloidal, with the filament substantially :at the focus, if/a parallel beam of light is desired; but for use in a slide or motion picture projector, the reflector-is generally made ellipsoidal with-the filament at the nearerffocus of the ellipse.

The reflector and filament are made in a unitary structure, with the lead-in wires 4, 5 which support the filament extending through a ceramic insulatingbushing 6 fixed to reflector 3 through an opening therein. In this Way the filament and reflector can be fixed in position with respect to each other before being fixed in position in the envelope 1. 'Thelatter has four stiff wire contact prongs 7, 8, 9 (the one which would be 10 is'not shown), sealed through the bottom or base 11 of the envelope 1.

A metal cap 35 fits around the base 11, extending up the'cylindrical wall 13 of envelope '1 and containing the downwardly-extendinghollow projection 14 which protects the sealed exhaust tubelS. Each contact prong 7, 8, 9 (and ill-not shown) has the glass beads 16, 17, sealed around it, and the metal cap 35 has holes through which said beads pass.

The cap 3'5 carries three spaced projections 15!, 20, 21 which cooperate with fingers in a socket to align the bulb therein. One said socket is shown in copending applica- 'tion Serial No. 553,367,'filed December 15, 1955, by William H. Morgan, J12, for a Lamp Positioner. The projection 14 has the key 22, as shown in-FIGJZ, extending parallelto the axis of the envelope, to aid in aligning the lamp in a socket.

The lead-in wires 4,5 extend directly only a short distance behind the bushing 6, the connecting Wire .12 being connected to wire 4 atthe back of bushing '6 and extending downward at anangle to be connected near its end to lead-in wire 8. The connecting wire 12 is bent crosswise to lead-in wire 8 to make a-more efiective supporting connection. Lead-in wire 10, not-shown,would be similarly connected to a support wire 18 between leadin wire 5 and a contact prong.

The'reflector-z has two eyeletted tabs 23, 24 and a short support wire 25, 26 is welded across the tab and welded also to the contact prongs 7, 9. This helps-align the reflector in the bulb and keeps it in position.

By running thelead-in wires 4, 5 through closelyfitting holes in the ceramic backing '6 arcing between the lead-inwi'res on filament burnout is prevented, and a fuse toprevent such arcs is unnecessary. hole through which the arc must pass-in the ceramic 6 snulTs-it out.

The filament 2 and its supports, 4, 5, areshown-in more detail in FIG. 3. The supporting wires- 4, 5 extend through the ceramic bushing 6 and .are bent outwardly as they emerge from said bushing on the con- -cave side of the reflector. This bending together with the welding of connecting wires 12, 18 to lead-in wires 4, 5 at the other end of the ceramic 6, helps keep the filament and reflector in permanent alignment.

The filament 2 itself is a coiled-coil having a tungsten wire 27 coiled into a primary coil 28 of small diameter with the middle length of the primary coil itself again coiled to form a coiled-coil 29 of larger diameter. The turns 30 and 31 are pulled out to a greater distance than the remainder of the coil for reasons previously explained. Each end portion 32, 33 of the coil has a mandrel 34, generally called a spud, fitted tightly inside it to facilitate welding or other connection to the lead-in wires 4, 5 and also to short the ends of the coil to keep them from being heated as much as the The narrow 3 remainder of the coil. For convenience in drawing, the spud is terminated at the beginning of the pulled-out turn, but in practice it will be desirable to have it near the middle of the turn, so that variations in the exact amount of insertion will not have much effect.

As an example of a coil according to the invention, the portion 32 would be about 6 turns long, and the portion 28 would be about 8 turns long, with five secondary turns in the coiled-coil portion 29. The latter portion has 30 turns per inch, and the spud 34 is a tungsten pin 0.030 inch in diameter. The primary coil was wound to 64 turns per inch on a -mil mandrel. The average primary coil diameter was 26.7 mils.

In the specific embodiment here described, the reflector had an elliptical curvature according to the following curve y =2(0.880)x--0.650.1c

where y is the vertical coordinate and x the horizontal bottom of the envelope.

The side of the coiled-coil filament nearest to the re flector is positioned 0.070 inch in front of the plane of the outer edges of the reflector, and that plane is 0.450 inch from the apex of the reflector, that is, from the apex of the reflector curve where it would pass through ceramic 6 if that ceramic were not there. These distances are shown as a and b respectively in FIG. 1.

In operation, a voltage of about 21.5 volts is connected between the filament contact prong 8 and the corresponding prong (not shown) to the other side of the filament. The contact prongs 7 and 9 are left float ing, that is, not connected to anything, because if they are connected to either side of the line, the reflector will blacken by conduction through the gas to the other end of the voltage supply line.

The graph of FIG. 4 shows the lamp efliciency in lumens per watt (L.P.W.) at the screen of a projector, plotted against the voltage at which the filament must be operated to obtain the rated life of hours. (The life in a projector lamp is customarily of that value in order to obtain high efliciency.) The filaments used were different for each voltage, but the wattage and overall dimensions of the filament were the same.

In other words, a series of filament coiled-coils were made, each coil being of 0.200 inch axial length and 0.085 inch outside diameter, each coil having the same number of secondary turns but differing in wire size. The number of primary turns was changed slightly to accommodate the different wire sizes. The lamps were all used in the same movie projector for 8 mm. film and the coil was made of the above size to insure that the objective lens would be completely filled with useful light for all coils tested. The lumens per watt at the screen on which the lens were focussed were then measured.

In that way, the best coil for efliciency was found to be one that gave the rated life at 21.5 volts. All other coils were less eflicient.

When the coil is designed for a voltage of about 100 volts or more, it can no longer be made of such dimensions as to fit within the 0.200 inch by 0.085 inch dimensions given above, and a coil for direct operation on a -volt line will have only about sixty percent of its turns within a rectangle of the dimensions given above. The light from the remaining turns will therefore not be useful in filling the usual projection lens with which the lamp would normally be used.

The tungsten wire of which the coil is wound had, in the specific example cited earlier in the present application, a diameter of about 8.48 mils. When wound in the manner described, the finished coiled-coil will have a diameter of about 0.085 inch.

What we claim is:

1. An incandescent projection lamp comprising a sealed enclosing bulb, an ellipsoidal reflector inside said bulb, and a coiled-coil tungsten filament in said bulb, said filament being of about 0.2 inch axial length and about 0.085 inch outside diameter adapted to attain its operating temperature at between about 20 and about 23 volts and being approximately at the focal point of said reflector nearest to said reflector.

2. An incandescent projection lamp comprising a sealed enclosing bulb, an ellipsoidal reflector inside said bulb, and a coiled-coil tungsten filamentin said bulb, said filament being of about 0.2 inch axial length and about 0.085 inch outside diamter adapted to attain its operating temperature at about 21.5 volts and being approximately at the focal point of said reflector nearest to said reflector.

3. An incandescent projection lamp comprising a sealed enclosing bulb, an ellisoidal reflector inside said bulb. and a coiled-coil tungsten filament in said bulb, said filament being of about 0.2 inch axial length and about 0.085 inch outside diameter designed to take about watts at 21.5 volts and being approximately at the local point of said reflector nearest to said reflector.

4. An incandescent projection lamp comprising a sealed enclosing bulb, an ellipsoidal reflector inside said bulb, and a coiled-coil tungsten filament at the approximate focus of said ellipsoidal reflector nearest to said reflector and being of about 0.2 inch axial length and about 0.085 inch outside diameter in said bulb, said filament having an opearting resistance between about 2.7 and 3.5 ohms.

5. An incandescent projection lamp comprising a sealed enclosing bulb, an ellipsoidal reflector inside said bulb, and a coiled-coil tungsten filament at the approximate focus of said ellipsoidal reflector nearest to said reflector and being of about 0.2 inch axial length and about 0.085 inch outside diameter in said bulb, said filament having an operating resistance of about 3.1 ohms.

References Cited in the file of this patent UNITED STATES PATENTS 654,208 Washburn et a1. July 24, 1900 1,790,086 Boerstler Jan. 27, 1931 2,424,518 Stuart July 22, 1947 2,795,722 Burgener et al June 11, 1957 2,820,920 Penon Ian. 21, 1958 

